Chapter 1: System Architecture

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  • Created by: ronelaM
  • Created on: 25-07-18 08:28
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  • Chapter 1: System Architecture
    • Computer system:
      • A computer system is able to take in inputs, process them and output them; the output is sommetimes stored.It does this using a varity of hardware and software. A computer system is comprised of the CPU, memory and other internal components, for example a GPU
      • The creation of the firts electronic general- purporse computer system began in 1943 and was completed in 1946; it was called ENIAC
    • Embedded system
      • An embedded system is normally built into a piece f machinery or device. It is a computer system that is desigen to  provide very limite and specific funcions. it mostly consists os a small microprocessor that provides a similar function to a CPU; it takes in an inut processes it and provides an output as a result.
      • Manufecturers use embedded systems in their devices fot a number os reasons:    -They allow the device to be programmed to automaticlly perform one or a small number of functions.       -They can reduce the size of the machinery or device.           -They can reduce the cost of the machinery or device.
      • A computer system that can perform many different functions is called a general- purpose computer. This type of computer had a central "brain" to allow it to perform all the different functions, which is called the CPU.
      • Examples of embedded systems are: cars, smoke detectors, washing machines, air conditioning, microwaves ect.
    • CPU
      • The purpose od the CPU is to process data and instructions. It is  where the decision makind takes place in a computer. Data and instuctions are transproted around the CPU through the use of buses. The CPU is made up of a number of component parts. There is a particular CPU structure that is called the Von Neumann architecture.
      • Arithmetic and logic unit (ALU):      The  ALU is the part of the CPU that carries out all he arithmetic and locgic operations. Data is passed to the ALU to allow the required calculations to be carried out. The results of any calculations are then send to be stored in a register.
      • Accumulator (ALU):            The accumulaor is the register where intermediate arithmetic and logic results are stored. It accumulates the results of the calculations.
      • Control Unit (CU):              The control unit is responsible for directing the flow of all inputs and outputs to the CPU. It controles the differeent stages of the execution of an instruction and it guides the flow of data through the different parts of the CPU. It also controls and monitors the hardware attached to the computer. It tells the ALU, the computer's memory and the hardware devices how to respond to an instruction. The CU communicate with the rest of the components by uding the control bus.
      • Memory address register (MAR):           The MAR holds the address location of the next piece of that data that is to be fetched into the CPU, or the address where a piece of data will be sent to be stored. The address location is sent to and from the MAR using the address bus.
      • Memory data register (MDR):           The MDR hold the actual data that is  being fetched into the CPU, or the data that is being sent to be stored in the computer's memory. The data is sent to and from the MDR using the data bus.
      • Program counter (PC): The program counter is a register that holds the address of the next instruction that is to be carried out. It is designed to indicate where the CPU is up to in a program sequence. There is alse a register that holds the address of the current instruction that is being processed; this is called the current instruction register (CIR).
      • Cache:           The cache is small section of memory that is built into the CPU. It is stored the most commonly used intructions and data to allow quick and easy access to them. There are three 'levels' of cache:             -L1 cache, typically operating at speeds close to the CPU.     -L2 cache, which is slightly slower and further away from the CPU                -L3 cache, is the cache memory furthest from the CPU, which runs slowest.
    • Fetch-execute cycle
      • The fetch-execute cycle is the process a CPU goes through in order to process an insttruction.At the start of the fetch-execute cycle, both the data and the instruction are loaded into the computer's main memory so they are ready to be processed. It is the computer's operationg system that loads them into place.
      • The instruction that are processed by the computer come in a specific from of binary vits. The actual instruction itself is split into two parts, the opcode and the operand.
      • Fetching an instruction:  The first step the CPU carries out is to fetch the instruction and data into the CPU. A value is placed in the PC to indicate the adddress of the instruction that is to be carried out. This value is then passed to the memory address register so that the instruction or data stored there can be located. The value is then sent to the memory to locate the address. This is done using the address bus. Any data stored in the memory address is then sent to the MDR using the data bus.
      • Decoding an instruction:    In order to decode an instruction, the CPU uses an instruction set. This is a set of commands that are written in machine language that the CPU understands.
      • Executing an instruction:    This is the part of the cycle where any actions required by the instruction take place, such as any calculations that need to be carried out using the data. The ALU may be used at this stage to carry out the calculation.
    • What can affect the performance of the CPU?
      • There are three main factors that can affect the performance of a CPU: these are the clock speed, the cache size, and the number of cores available to the CPU.
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